Case Study: Copper mining at Tonderghie

What evidence is there for prospecting and mining for copper ores during the Bronze Age in Scotland? Some of the problems in identifying early metal mining sites are demonstrated by the site at Tonderghie, a small copper deposit near Whithorn, Dumfries and Galloway.

At Tonderghie a vein of barite with some copper mineralisation - mainly chalcopyrite and malachite - is exposed in coastal cliffs. This is one of a number of small copper deposits in south-west Scotland which were exploited during the post medieval period. Surviving surface remains, all assumed to be eighteenth or nineteenth century in date, include two in-filled mine shafts, a collapsed adit level and some areas of spoil. There is also an undated opencast working on the vein itself. Some of the mine workings overlay an area of rig cultivation.

Tonderghie is unique in having strong circumstantial evidence for earlier, possibly prehistoric, phases of mining. The Old Statistical Account of Whithorn parish compiled in 1794 refers to 'six pieces (of copper) in an earthen vessel' found on the Tonderghie estate and an accompanying illustration of one of these objects indicates that this was a hoard of EBA copper ingots. The same account also describes the discovery on the estate of a circular copper ingot which by its size and weight appears to be a late prehistoric or Roman bun ingot. Another bun ingot was found in 1880 at Carleton some 5km north west of Tonderghie. These ingots suggest the exploitation of a local ore source and Tonderghie, as the only copper vein in the immediate area, is the most likely site.

Recent fieldwork (Pickin and Hunter 2008) at Tonderghie has attempted to identify evidence for early exploitation. Over the last thirty years a number of Bronze Age mines have been recognised and recorded in Ireland, Wales and England. All these mines have produced a range of distinctive stone tools which were used in hard rock mining and ore processing; these tools are often found in association with mine spoil and fire-setting residues. Despite detailed searches on a number of occasions no stone tools have been found at Tonderghie nor have any stone tools from the site been identified in local museum collections. A detailed topographical survey by RCAHMS recorded the post-medieval mining features and the earlier, but probably still post medieval, field system. The survey also recorded some enigmatic earthworks, possibly related to ore extraction and processing, but their relationship to the field system and later mining features could not be established. Geophysical survey of the same area highlighted several features of archaeological significance including a feature close to the opencast interpreted as a circular ditched enclosure and the traces of another circular structure or hollowed feature, defined by a stone bank or wall, overlain by one of the post medieval mine shafts. Both the topographical and geophysical surveys suggest activity at the site predating the post medieval field system but further interpretation and dating can only be achieved through archaeological excavation.

The Tonderghie survey also included geochemical work by Dr T Mighall (2003), Aberdeen University. Elsewhere in the UK evidence for early mining has been reconstructed using geochemical proxies from peat bogs. For instance at Toddle Moss, near Leadhills, several phases of lead enrichment have been identified in the LBA, the tenth century AD and during later historical times. Lead isotopic signatures suggest that the lead is derived from local sources. A similar methodology was employed at Tonderghie. A 2.85 metre deep core was collected using a Russian corer for palaeoenvironmental analysis from a valley marsh that had grown in the infilled leg of a small lochan within 700 metres of the mine. A radiocarbon assay produced a calibrated age range of Cal BC 2834-2472 at 120 cm depth and Pb-210 dating has provided a chronology for the upper 40 cm of the core. Further geochemical analysis is planned to identify pollution phases and pollen analytical work to reconstruct vegetation changes associated with the mine.

The historic finds of EBA and late prehistoric ingots coupled with the results of the recent survey indicate that Tonderghie has the potential to be an early mine. Frustratingly, that evidence is still inconclusive and further work is required to establish the date and significance of the site.